PETSC-Hypre: number of level with boomeramg

[Barry Smith]

On Thu, 25 Jan 2007, Fernando Campos wrote:

> Dear Nicolas, 
> 
> It is a good question, but I don't know the answer... 
> Why don't you try to set the maximum levels to a large numbers in order to 
> see how many levels boomerAMG creates? I believe that it refines the grid up 
> to the maximum number of levels as you sad. 
> 
> I am very interested in both geometric and algebraic multigrids and I also 
> have a question: "Is it possible to obtain the coarse matrices of each level 
> using boomerAMG?" 

  In the PETSc the coarse matrices are left in hypre format so we do not 
have direct access to print them out. You would have to futz around in the hypre
data structures to fine them (if you did this we'd love if you could contribute
the code to print them out to PETSc.).

  Barry


> 
> Best Regards. 
> 
> 
> Em (15:31:40), petsc-users at mcs.anl.gov escreveu: 
> 
> 
> >Dear Fernando, 
> > 
> >Thanks for your reply. 
> > 
> >I had notice the value maxlevels given by -ksp_view, but I did not know 
> >how to change this value. 
> > 
> >Still, as the default is 25 levels I think, I have no way to know exactly 
> >how many levels are used for a given case. 
> >I can reformulate my question in this way: does boomeramg coarsen the 
> >"grid" to the coarsest level possible, i.e. 1 cell over the domain, or 
> >does it stop before that? (grid is not the right term when it comes to 
> >algebraic multilevel methods, but I can't find any other clear way to 
> >express it). How can I control the coarsening? 
> > 
> >Thinking about it, perhaps boomeramd actually refines the grid up to the 
> >maximum number of levels...Is it so? 
> > 
> >Thanks for your help. 
> > 
> >Nicolas 
> > 
> >> Nicolas, 
> >> 
> >> You should try the option -pc_hypre_boomeramg_max_levels in the line 
> >> command. In order to see the level's details you can use the PESTc option 
> >> -ksp_view. 
> >> 
> >> Best Regards 
> >> 
> >> Fernando. 
> >> 
> >> 
> >> Em (11:15:45), petsc-users at mcs.anl.gov escreveu: 
> >> 
> >> 
> >>>Hi Petsc users, 
> >>> 
> >>>I have a question regarding the use of Hypre and especially Boomeramg. 
> >>>How can we control the number of levels in the multigrid algortihm? Can 
> >>> we 
> >>>chose it, or if not, can we display it in some way? 
> >>> 
> >>>Best regards, 
> >>> 
> >>>Nicolas. 
> >>> 
> >>>-- 
> >>>Nicolas BATHFIELD 
> >>>Chalmers University of Technology 
> >>>Shipping and Marine Technology 
> >>>phone: +46 (0)31 772 1476 
> >>>fax: +46 (0)31 772 3699 
> >>> 
> >>>---------- 
> >> 
> >> 
> >> 
> > 
> >-- 
> >Nicolas BATHFIELD 
> >Chalmers University of Technology 
> >Shipping and Marine Technology 
> >phone: +46 (0)31 772 1476 
> >fax: +46 (0)31 772 3699 
> > 
> >---------- 
> 
> 
>